Motion tracking round objects
As cegaton mentioned your current solution does not represent 3d space, because you don't have enough trackers. You can try the following workflow:


First enable object tracking 





Try to track the head with 8-14 markers
Increase the search area of the markers, if the footage is jumpy 
Solve your object track with a value bellow 0.6
Apply a camera solver constraint to the scene camera without solving it, this  should show your object solution (calculated empties) in the viewport





Align your new face geometry to the empties (trackers) or use the trackers to pointcloud function to reconstruct the head  
Apply an object solver constraint to the new geometry 




Now your object hopefully should move properly with the empties.